microstrip to waveguide transition arrangement

ABSTRACT

The present invention relates to a transmission line to waveguide transition arrangement comprising a dielectric carrier material arrangement having a first main side and a second main side, the arrangement comprising a transition portion with an opening, having at least one edge and an electrically conducting border which follows the opening and is electrically connected to a ground metalization on the second main side. A transmission line conductor extends in the dielectric carrier material arrangement towards the border. The arrangement further comprises a transitional part with a border contact section having an outer circumference that essentially follows the border&#39;s shape except for a gap dividing the border contact section. The transitional part further comprises a conductor contact section which protrudes from the border contact section through the gap, contacting the end of the transmission line conductor and extending into the opening.

TECHNICAL FIELD

The present invention relates to a microstrip to waveguide transitionarrangement comprising a dielectric carrier material arrangement havinga first main side and a second main side, the arrangement comprising atransition portion which in turn comprises an opening, having at leastone edge, and an electrically conducting border, which border followsthe opening and is electrically connected to a ground metalization onthe second main side, where a transmission line conductor extends in thedielectric carrier material arrangement towards the border.

BACKGROUND

When designing microwave circuits, microstrip transmission lines arecommonly used. A microstrip transmission line comprises a metal groundplane and a conductor, where a dielectric carrier material is positionedbetween the metal ground plane and the conductor. This configuration iseconomical and relatively easy to design.

Another type of transmission line is a stripline conductor. Here, aconductor is sandwiched between two dielectric carrier materials, whereground planes are placed on the sides of the dielectric carriermaterials that face away from the conductor.

Yet another type of transmission line is a co-planar conductor, where aconductor is placed on a dielectric carrier material and ground planesare placed on the same side of the dielectric carrier material as theconductor, surrounding it, with a small gap between the ground plane andthe conductor.

However, due to losses in the dielectric carrier material, it issometimes not possible to use any of the transmission lines above. Whenthere for example is a filter in the layout, the filter may have to berealized in waveguide technology. Waveguides are normally filled withair or other low-loss materials.

When there is a filter in a microwave circuit microstrip layout, thefilter may thus be realized by means of a waveguide filter in order tolower the losses. In that case, there has to be corresponding microstripto waveguide transitions at the ends of the filter. Such a waveguide ispreferably surface-mounted, enabling it to be mounted to the dielectriccarrier material.

Such a surface-mounted waveguide is normally made having three walls andone open side. Metalization is then provided on the side of thedielectric carrier material facing the waveguide, where the metalizationserves as the remaining wall of the waveguide, thus closing thewaveguide structure when the waveguide is fitted to the dielectriccarrier material.

Another application for surface-mounted waveguides is when there has tobe a microstrip to waveguide transition in the form of a bend, allowinga waveguide to be mounted to the dielectric carrier material in such away that it extends essentially perpendicular to the main surfaces ofthe dielectric carrier material.

It is also conceivable that a waveguide filter is realized having aseparate fourth closing wall made as a metalization on a dielectriccarrier material, where such a design is found cost-effective.

It is of course also common that it is desired to have a transition froma transmission line to a general waveguide interface.

A special case regarding surface-mountable waveguides is disclosed inthe paper “Surface-mountable metalized plastic waveguide filter suitablefor high volume production” by Thomas J Müller, Wilfried Grabherr, andBernd Adelseck, 33^(rd) European Microwave Conference, Munich 2003.Here, a surface-mountable waveguide is arranged to be mounted on aso-called footprint on a circuit board. A microstrip conductor towaveguide transition is disclosed, where the end of the microstripconductor acts as a probe for feeding the waveguide's opening. Themicrostrip conductor is in contact with the waveguide via a steppedridge, which matches the impedance in the transition. Furthermore, thetransition region is bordered by via holes.

There is, however, a problem with the design according to said paper, aswell as with general transitions from a transmission line to a waveguideinterface, since a microstrip probe is carried by the circuit board,causing losses, and since there is a need of via holes, defining anelectric wall through the circuit board.

There is thus a demand for a waveguide arrangement comprising atransmission line to waveguide transition that provides lower losses anda less expensive and simpler design.

SUMMARY

The object of the present invention is to provide a waveguidearrangement comprising a transmission line to waveguide transition whichprovides lower losses and a less expensive and simpler design.

This problem is solved by means of a waveguide arrangement as mentionedinitially. Said arrangement further comprises a transitional part whichin turn comprises a border contact section having an outer circumferencethat essentially follows the shape of the border except for a gap whichdivides the border contact section where it faces the end of thetransmission line conductor, where the transitional part furthercomprises a conductor contact section which protrudes from the bordercontact section through the gap, in such a way that it contacts the endof the transmission line conductor and extends into the opening, fromthe transmission line conductor towards the border contact section.

According to a preferred embodiment, the ground metalization on thesecond main side is arranged for contacting a waveguide part which ismounted to the transition portion, where the ground metalization on thesecond main side is arranged to receive a waveguide flange.

According to another preferred embodiment, the dielectric carriermaterial consists of one dielectric layer, where the transmission lineis a microstrip conductor or a co-planar conductor.

According to another preferred embodiment, the dielectric carriermaterial comprises at least two dielectric carrier layers, where thetransmission line is a stripline conductor.

According to another preferred embodiment, the transitional part has anopen structure facing away from the opening when the transitional partis mounted to the dielectric carrier material arrangement, where theopen structure may be covered by a lid.

A number of advantages are provided by the present invention. Forexample:

-   -   there is no need for a probe;    -   a microstrip to waveguide transformer and a wave-guide bend are        combined into one item, being constituted by the transitional        part;    -   there is no dielectric material in the wave-guide opening, which        reduces losses;    -   very little area on the dielectric material arrangement is        occupied by the transitional part; and    -   enhanced soldering alignment is achieved since the transitional        part may align to the border pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described more in detail withreference to the appended drawings, where:

FIG. 1 shows a top perspective view of a dielectric carrier arranged forthe present invention;

FIG. 2 a shows a top view of the transitional part according to thepresent invention;

FIG. 2 b shows a side view of the transitional part according to thepresent invention;

FIG. 3 shows a first type of a waveguide part used with the presentinvention;

FIG. 4 a shows a bottom view of a second type of a waveguide part usedwith the present invention;

FIG. 4 b shows a side view of a second type of a waveguide part usedwith the present invention;

FIG. 4 c shows an end view of a second type of a waveguide part usedwith the present invention, mounted to a dielectric carrier material;

FIG. 4 d shows a side view of a second type of a waveguide part usedwith the present invention, mounted to a dielectric carrier material;

FIG. 5 shows a top perspective view of an alternative for a dielectriccarrier arranged for the present invention;

FIG. 6 shows a top view of a first alternative for the transitional partaccording to the present invention;

FIG. 7 shows a top view of a second alternative for the transitionalpart according to the present invention;

FIG. 8 a shows a side view of a third alternative for the transitionalpart according to the present invention, adapted for a striplinearrangement;

FIG. 8 b shows a side view of the third alternative for the transitionalpart according to the present invention mounted to a striplinearrangement;

FIG. 8 c shows a top view of a stripline arrangement according to thethird alternative for the transitional part according to the presentinvention; and

FIG. 9 shows a side view of an alternative transitional part accordingto the present invention.

DETAILED DESCRIPTION

In FIG. 1, showing a first embodiment example of the present invention,a dielectric carrier material 1 is shown, having a first main side 2 anda second main side 3, originally having a metallic copper cladding onboth sides. The copper on the second main side 3 is used as a groundplane, and the copper on the first main side 2 is etched away to such anextent that desired copper patterns are formed on the first main side 2.These copper patterns may for example form a microwave circuit layout,e.g. microstrip transmission line conductors and footprints forcomponents which are intended to be soldered to the dielectric carrier(not shown).

A transition portion 4 is formed on the first main side 2 of thedielectric carrier 1, being intended for use as a transition from amicrostrip transmission line conductor 5 extending on the first mainside 2 to a waveguide part (not shown in FIG. 1) such that a waveguideport, lying in the dielectric carrier's plane and facing 90° away fromthe longitudinal extension of the microstrip transmission line conductor5, is formed. The transition portion 4 comprises an opening 6 which hasan essentially rectangular shape, having a first edge 7, a second edge8, a third edge 9 and a fourth edge 10, where the corners are slightlyrounded due to manufacturing methods, and the edges 7, 8, 9, 10 arefacing inwards the opening 6. The fourth side 10 faces the incomingmicrostrip conductor 5.

The transition portion 4 comprises a border 11 of copper, having acertain width, which border 11 follows the opening's edges 7, 8, 9, 10.The border 11 is electrically connected to the ground plane on thesecond main side 3 via copper plating on the opening's edges 7, 8, 9,10. In this embodiment, the microstrip conductor 5 extends towards theborder 11, but stops a short distance before the border 11, not makingelectric contact.

According to the present invention, with reference to FIG. 2 a and FIG.2 b, in order to achieve a microstrip conductor to waveguide transition,the waveguide transition arrangement comprises a transitional part 12which is adapted to be mounted to the border 11, having a border contactsection 13 that essentially follows the shape of the border 11 exceptfor a gap 14, dividing the border contact section 13 where it faces theend of the microstrip conductor 5 when mounted to the border 11. Theborder contact section 13 thus comprises a first wall 15, a second wall16, a third wall 17 and a fourth wall 18, where the fourth wall 18 ofthe border contact section lies against the fourth edge 10 of theopening 6 when mounted to the border 11, and the second wall 16 isopposite the fourth wall 18, where the gap 14 is situated on the middleof the fourth wall 18.

The walls 15, 16, 17, 18 define a first continuous surface 19, arrangedto face the border, and a second continuous surface 20, arranged to faceaway from the border 11, when the transitional part 12 is mounted to theborder 11.

The transitional part 12 further comprises a conductor contact section21 which protrudes from the middle of the second wall 16, through thegap 14, in such a way that it contacts the end of the microstripconductor 5 when the transitional part 12 is mounted to the border 11.

The conductor contact section 21 has a height perpendicular to the mainextension of the second wall 16 and a width that corresponds to thewidth of the microstrip conductor 5.

The following relates to the case where the transitional part 12 ismounted to the border 11. The conductor contact section 21 has a contactpart 21 a that is arranged to be in the same level as the microstripconductor 5, the level being essentially the same as the level of thefirst surface 19. Then follows a raised part 21 b, being raised relativeto the dielectric carrier 1 such that contact with the dielectriccarrier 1, and thus the border 11, is avoided. Then follows a steppedpart 21 c, comprising steps extending past the level of the firstsurface 19, into the opening 6.

The side 22 of the conductor contact section 21 opposite the one thatcontacts the microstrip conductor lies in the same level as the secondsurface 20.

The use of such a stepped structure in a microstrip to waveguidetransition is well-known in the art, and will not be discussed more indetail here.

An example of a first type of waveguide part 23 arranged to be mountedto the transition arrangement according to the present invention isshown in FIG. 3. Such a waveguide part is constituted by a waveguideflange 24 that is arranged to be mounted to the second main surface 3 ofthe dielectric carrier 1, and a waveguide tube 25 which may extend awayfrom the dielectric carrier 1, the waveguide tube 25 being shown cutopen for explanatory reasons. The waveguide part 23 is hollow with across-sectional aperture 26, the cross-sectional aperture 26 having acertain dimension that depends on the frequency for which the waveguidepart 23 is intended to be used. The flange 24 is shown mounted to theopening 6 (not shown in FIG. 3) in the dielectric material 1, theopening 6 forming a waveguide contact interface, or waveguide port, onthe second side 3 of the dielectric carrier 1. The opening 6 has adimension that corresponds to the waveguide's cross-sectional aperture26. The transitional part 12 is mounted to the border as discussed above(not shown).

A second type of waveguide part arranged to be mounted to the transitionarrangement according to the present invention is shown in FIG. 4 a-4 d.Here, a surface-mounted waveguide part 27 is used instead, being mountedto the second main 3 side of the dielectric carrier 2. Thesurface-mounted waveguide part 27 is constituted by an open waveguidetube 28 having only three closed walls 28 a, 28 b, 28 c, leaving oneside 28 d open. The tube 28 has an interface portion 29 which isintended to be mounted to a waveguide port, functioning as a flange. Thewaveguide tube 28 performs a 90° turn directly after the interfaceportion 29 such that it is arranged to be mounted to the second mainsurface of the dielectric carrier, the interface portion 29 beingequipped with a stepped portion in a well known manner. The open side 28d is intended to be closed when the second type of waveguide part 27 ismounted to the second main surface 3 of the dielectric carrier 1. Theextension of the waveguide tube 28 is limited by a broken line, sinceits further functions are of no interest for the present invention.

When mounted, the second waveguide part's waveguide tube 28 is hollowwith a cross-sectional aperture 30, the cross-sectional aperture 30having certain dimensions that depend on the frequency for which thewaveguide part is intended to be used. The interface portion 29 ismounted to the opening 6 (not shown in FIG. 4 d) in the dielectricmaterial 1, the opening 6 forming a waveguide contact interface, orwaveguide port, on the second side 3 of the dielectric carrier 1. Theopening 6 has a dimension that corresponds to the waveguide'scross-sectional aperture. The mounting is performed by means of mountingrims 31 running along the open waveguide tube.

Such a surface-mounted waveguide part is previously known, its detailswill not be discussed further here.

The present invention is not limited to the embodiment described above,but may vary freely within the scope of the appended claims.

For example, with reference to FIG. 5, an alternative border 11′ may beequipped with a gap 32 that corresponds with the one in the transitionalpart's border contact section 13, allowing an alternative microstripconductor 5′ to pass the border and end just before the opening's 6fourth edge 10. In this way, the transitional part's conductor contactsection may have an alternative shape, not having to extend over theborder, but can be made shorter.

Furthermore, with reference to FIG. 2 a, inside the inner boundaries ofthe second surface 20, there is an open structure 33 facing away fromthe opening in the dielectric carrier 1 when the transitional part 12 ismounted to the dielectric carrier material 1. Optionally, with referenceto FIG. 6, showing a top view of another alternative design of thetransitional part 12′, this open structure may be covered by means of anelectrically conducting lid 34 which covers the open structure, withoutcontacting the conductor contact section 21′, thus reducing the amountof microwave radiation escaping through the open structure.

With reference to FIG. 7, showing a top view of another alternativedesign of the transitional part 12″ the border contact section 13″ ismade massive, having no open structure, not needing any lid.

All mountings above are preferably performed by means of soldering, butof course other alternatives are possible, for example gluing withelectrically conducting glue.

The transitional part may be made in one piece or by several pieces. Inthe latter case, all pieces should be in electrical contact.

The opening which essentially corresponds to the waveguide'scross-sectional aperture is of course adapted to the shape of thewaveguide used. The opening is thus circular if a circular waveguide isused. Manufacturing methods also give rise to different shapes of theopening and the used waveguide's cross-sectional aperture, the smallerthe opening is, the larger radius the rounded corners will have. Allrelated parts, such as the transitional part and the border are shapedcorrespondingly.

The waveguide parts disclosed, including the transitional part, whichfor example may be made in metal or metallised plastics, are only twoexamples of a variety of waveguide parts that may be used with thepresent invention, which in itself does not include any specialwaveguide part, but only is arranged to interact with a waveguide part.

The exact measures of the parts described, for example the number ofstep of the stepped part and the steps' measures depends on thefrequency used and which characteristics the design shall have. Thesedetails are not a part of the present invention, and can be derived foreach specific design by the skilled person. The essence of the presentinvention is to use a transitional part for a transmission line towaveguide transition, the transitional part enabling the use of anopening in the dielectric carrier, thus dispensing with via holes andthe presence of a lossy dielectric material at the waveguide transition.

The transmission line may be of any suitable kind, such as microstrip,stripline or co-planar. With reference to FIG. 8 a, showing analternative design of the transitional part 12′″ adapted to be used fora stripline to waveguide, the transitional part's conductor contactsection 21′″ has a contact part 21 a′″ that is modified for striplineuse. With reference to FIG. 8 b, a section across an opening 35 in astripline arrangement 36 to which the transitional part 12′″ is mountedis shown. The stripline arrangement comprises a first dielectric carriermaterial 37 and a second dielectric carrier material 38 and a conductor39 which is sandwiched between the dielectric carrier materials 37, 38.

The transitional part's conductor contact section 21′″ is arranged toextend past the first dielectric carrier material 37, such that itcontacts the conductor 39. There is thus an access opening 40 throughthe first dielectric carrier material 37, allowing the contact part 21a′″ to reach the conductor 39. A top view of the stripline arrangement36 without the transitional part 12′″ is shown in FIG. 8 c.

The stripline arrangement also comprises copper ground planes 41, 42 onthe sides of the dielectric carrier materials 37, 38 which face awayfrom the conductor 39. The opening 35 is copper plated in such a waythat the ground planes are in electrical contact.

For all embodiments, any suitable metal or alloy may be used for theconducting parts, copper has been mentioned, and examples of othersuitable metals are silver and gold.

All conducting structures on the dielectric carrier materials aresuitably made by means of etching, although other processes such asscreen-printing also are conceivable.

The dielectric carrier material 1 may comprise several dielectricmaterials, thus constituting a dielectric material arrangement. In casesof multilayer arrangements for the dielectric carrier, such as astripline arrangement which comprises two dielectric carrier materials,such a dielectric carrier material arrangement still comprises a firstmain side and a second main side, where the main sides are those thatare not adjacent to any other side, i.e. those which face away from thedielectric carrier material arrangement. For example, in the striplinecase above, the sides carrying the ground planes are the first andsecond mains ides.

Where the conductor is embedded, such as in the stripline case, thewaveguide transition part is adapted for this as described above.

The copper plating on the opening's edges 7, 8, 9, 10 may be constitutedby any appropriate electrically conducting element.

Even though it may make the design less simple, it is of course possibleto electrically connect the border 11 to the ground plane on the secondmain side 3 by means of any other suitable means than plating, forexample by means of vias.

Furthermore, the stepped structure may for an alternative transitionalpart 12″″ be replaced with a continuous structure 43, having an arcuateshape, as shown in FIG. 9.

The conducting parts, in particular the ground plane and the border, mayhave any suitable shape. The border has to follow the opening and theground plane may be any suitable ground metalization. The border iselectrically connected to the ground metalization on the second mainside via an electrically conducting plating on said edge.

1. A transmission line to waveguide transition arrangement comprising adielectric carrier material arrangement having a first main side and asecond main side, the arrangement comprising a transition portion whichin turn comprises an opening having at least one edge, and anelectrically conducting border, wherein the border follows the openingand is electrically connected to a ground metalization on the secondmain side, where a transmission line conductor extends in the dielectriccarrier material arrangement towards the border, wherein the arrangementfurther comprises a transitional part which in turn comprises a bordercontact section having an outer circumference that essentially followsthe shape of the border except for a gap which divides the bordercontact section where it faces the end of the transmission lineconductor, where the transitional part further comprises a conductorcontact section which protrudes from the border contact section throughthe gap in such a way that it contacts the end of the transmission lineconductor and extends into the opening, from the transmission lineconductor towards the border contact section.
 2. A transmission line towaveguide transition arrangement according to claim 1, wherein theground metalization on the second main side is arranged for contacting awaveguide part which is mounted to the transition portion.
 3. Atransmission line to waveguide transition arrangement according to claim2, wherein the ground metalization on the second main side is arrangedto receive a waveguide flange.
 4. A transmission line to waveguidetransition arrangement according to claim 1, wherein the dielectriccarrier material comprises one dielectric layer.
 5. A transmission lineto waveguide transition arrangement according to claim 4, wherein thetransmission line is a microstrip conductor, where there is a groundplane for the microstrip conductor on the second main side.
 6. Atransmission line to waveguide transition arrangement according to claim4, wherein the transmission line is a coplanar conductor.
 7. Atransmission line to waveguide transition arrangement according to claim1, wherein the dielectric carrier material comprises at least twodielectric carrier layers.
 8. A transmission line to waveguidetransition arrangement according to claim 7, wherein the transmissionline is a stripline conductor.
 9. A transmission line to waveguidetransition arrangement according to claim 1, wherein that thetransmission line extends towards the border without contacting it. 10.A transmission line to waveguide transition arrangement according toclaim 1, wherein the border has a gap through which the transmissionline extends.
 11. A transmission line to waveguide transitionarrangement according to claim 1, wherein the transitional part has anopen structure facing away from the opening when the transitional partis mounted to the dielectric carrier material arrangement.
 12. Atransmission line to waveguide transition arrangement according to claim11, wherein the open structure is covered by a lid.
 13. A transmissionline to waveguide transition arrangement according to claim 1, whereinthe transitional part is made in an electrically conducting metal.
 14. Atransmission line to waveguide transition arrangement according to claim1, wherein the transitional part is made in an electrically insulatingmaterial covered with a layer of electrically conducting material.
 15. Atransmission line to waveguide transition arrangement according to claim1, wherein the border is electrically connected to a ground metalizationon the second main side by means of an electrically conducting platingon the opening's edges.
 16. A transmission line to waveguide transitionarrangement according to claim 1, wherein the border is electricallyconnected to a ground metalization on the second main side by means ofvia holes.